Non-invasive prenatal screening for certain abnormalities in fetalchromosomes should be offered to at-risks mothers, recommends the American College of Obstetricians and Gynecologists (ACOG). The opinion has been well-received by companies that offer the technology for this test.

'We are very encouraged that ACOG is recognising the demand and the promise of non-invasive prenatal testing and how it is going to improve care for pregnant mothers', says Jonathan Sheena, chief technology officer for the California-based prenatal DNA testing company, Natera.

Fetal DNA can be found in the maternal bloodstream, outside of cells, and can therefore be tested for chromosomal abnormalities without the use of an invasive procedure that carries a small risk of miscarriage. The technology behind cell-free fetal DNA testing is still being evaluated. However, data collected so far suggests it is useful for at-risk mothers in the detection of fetal trisomy – a genetic defect where there are three copies of a particular chromosome, instead of two.

Women considered at-risk include those over the age of 35 years, those who have a history of a child with a trisomy and those whose fetal ultrasound scans suggest a chromosomal abnormality may be present. The test was not recommended as routine clinical practice and was not suggested for low-risk women or those carrying multiple fetuses, due to a lack of data to validate its use in these groups as yet.

The ACOG state, in their committee opinion released jointly with the Society for Maternal-Fetal Medicine Publications Committee, that cell-free fetal DNA testing 'does not replace the precision obtained with diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, and currently does not offer other genetic information'.

The test can only detect three conditions; trisomy 13 that causes Patau's syndrome, trisomy 18 that causes Edwards' syndrome and trisomy 21 that causes Down's syndrome. A positive test result should still be confirmed using CVS or amniocentesis, reports the ACOG.

The committee opinion concludes: 'To offer a cell free fetal DNA test, pretest counseling regarding these limitations is recommended. The use of a cell free fetal DNA test should be an active, informed choice and not part of routine prenatal laboratory testing'. As cell-free fetal DNA testing is still under development it is not currently available on the NHS.

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